The present invention relates to an element of a rotating drill pipe string.
In the field of exploration and working of petroleum deposits, rotating drill pipe strings are used, these consisting of pipes and other tubular elements which are joined together, end to end, according to the drilling requirements.
Such pipe strings may allow, in particular, sidetracked holes to be produced, i.e. holes whose inclination with respect to the vertical or the azimuth direction may be varied, during drilling.
In the case of highly offset sidetracked holes having horizontal or almost horizontal portions, the friction torques due to the rotation of the drill string may reach very high values during drilling. The friction torques may bring into question the equipment used and/or the drilling objectives. Furthermore, it is often very difficult to bring up the cuttings produced by the drilling, on account of the sedimentation of the debris produced in the drill hole, in the bottom part of the drill hole near the drill bit. This results in poor cleaning of the hole and an increase both in the friction coefficients of the pipe string pipes inside the drill hole and in the areas of contact between the pipes and the walls of the hole.
In order to decrease the friction coefficient and the area of contact between the pipe string and the walls of the hole, it has been proposed to use devices comprising a sleeve which may be mounted on the pipe string so that the pipe string can rotate inside the sleeve which itself comes into contact with the wall of the drill hole and which is thus rotationally immobilized. The sleeve constitutes a bearing inside which the pipe string is mounted so as to be able to rotate.
The area of contact between the pipe string and the wall of the hole is limited to the regions of contact of the rotationally immobilized sleeves with the wall of the drill hole, the sleeves having an overall outside diameter greater than the diameter of the pipes of the drill string. Grooves are generally provided on the outside surface of the rotationally immobilized sleeves, which grooves may be of helical shape and allow circulation of the drilling mud in the annular space between the wall of the drill hole and the pipe string. Because of the fact that they are rotationally immobilized, the sleeves do not make it possible to activate the circulation of the drilling fluid entraining the debris produced by the drill bit. The role of the known devices is therefore limited to reducing the friction between the pipes and the drill hole.
Moreover, drill pipes or tubulars are known which include on their external surface grooves of helical shape, these pipes or tubulars being rotationally driven with the pipe string. However, these parts of the drill pipes in the form of an Archimedean screw are not designed to promote the entrainment of the drilling fluid and of the debris suspended in this fluid, but to remedy the risks of differential-pressure sticking in the drill hole.